Biotin (vitamin H) is a kind of vitamin B and is related to fatty acid synthesis or saccharide metabolism as a coenzyme of a carboxylase. About 10 tons of biotin has been produced by chemical synthesis processes every year for use as a raw material for medicaments or cosmetics, feed additives, etc. However, because these processes are complicated, biotin is very expensive. On the other hand, biotin production by fermentation processes has been studied for a long time. The fermentation processes have not become practical because their productivity is low.
Biotin production using gene manipulation techniques has been expected to provide inexpensive biotin. Some microorganisms modified by gene engineering techniques have been used for biotin production. For example, microorganisms belonging to the genus Escherichia such as a strain resistant to .alpha.-dehydrobiotin disclosed in e.g. JP-A 61-149091 are known as the modified microorganisms for the biotin production. Other known modified microorganisms for the biotin production include microorganisms belonging to the genus Bacillus modified by transforming Bacillus sphaericus and then providing resistance to thenoyltrifluoroacetone (JP-A 4-11894), microorganisms belonging to the genus Serratia modified by providing Serratia marcescens SB411 with ethionine-resistance followed by S-aminoethylcysteine-resistance and then transforming the resulting microorganism with a recombinant plasmid containing a biotin gene fragment (JP-A 5-199867), transformants of Serratia marcescens SB411 provided with resistance to actithiazic acid, a compound having biotin-like structure, or resistance to 5-(2-thienyl)-n -valeric acid (JP-A 2-27980), and transformants provided with resistance to a nicotinic acid analogue (Japanese Patent Application No. 6-311778).
However, the prior art processes for producing biotin are unsatisfactory for the industrial production of biotin. There is still a need for a process for producing biotin having increased biotin productivity.